Manufacture of calcium carbide in shaft furnace



March 31,1959 s. KOOPAL 2,880,069

MANUFACTURE OF CALCIUM CARBIDE IN SHAFT FURNACE FIGJ INVENTOR.

BY A M 8 v- W.

S. KOOPAL March 31, 1959 MANUFACTURE OF CALCIUM CARBIDE IN SHAFT FURNACE2 Sheets'-Sheet 2 Filed May 5, 1955 INVENTOR.

Sp'e d8 Kypp al YW M '1 M444, ATTORNEYQ.

United States Patent MANUFACTURE OF CALCIUM CARBIDE IN SHAFT FURNACESieds Koopal, Sittard, Netherlands, assignor to Stamicarbon N. Heerlen,Netherlands Application May 5, 1955, Serial No. 506,333

application Netherlands May 7, 1954 6 Claims. (Cl. 23-208) Claimspriority,

The present invention relates to novel improvements in the manufactureof calcium carbide in a shaft furnace by burning therein, i.e., heatreacting, a solid fuel which consists essentially of carbon, preferablycoke, and lime or limestone which is also referred to hereinafter aslime. The high temperature and energy needed for the carbide formationis produced by burning part of the carbon present with an oxygen-richblast which is injected into the hearth of the furnace through tuyeres,the carbide formed being discharged in the liquid state from the bottomof the furnace, while the gas produced therein is discharged through thefurnace top. (See, for example, U.S. patent application Serial No.302,614, filed August 4, 1952, now abandoned.)

When operating in the manner described above, using thoroughly mixedcharges of, for example, one part of lime and two parts of coke, it hasbeen found that carbide with a CaC content of 60-70% can be continuouslyprepared if a small furnace (such as one having an internal diameter of56 cm. and a bed height of 2.5 m.) is used. However, when using a largerfurnace (e.g., internal diameter 80 cm., height of bed 2.5 m.) underotherwise identical operation conditions, certain unexpected difii-Culties are encountered. For instance, it has been found that due to ashell formation consisting substantially of lime over, and partly infront of, the burners, the condition of the hearth is deteriorated tosuch an extent that hardly any carbide can be produced.

Accordingly, the principal object of the present invention is to providenovel improvements in the abovementioned process whereby saiddifiiculties, and particularly undesired shell formation, are avoided.Other objects will also be hereinafter apparent from the ensuingdescription and accompanying drawings.

According to the present invention, the manufacture of calcium carbideby heat reacting lime, as such or in the form of limestone, and a fuelconsisting essentially of carbon, in a shaft furnace using a gas blastcontaining a high oxygen content to gasify the fuel and give thetemperature and energy necessary for carbide formation is improved bybuilding up the charge of lime and fuel in the furnace in such a waythat the concentration of the lime in a plane immediately above thetuyere mouths will increase from the furnace wall towards the center ofthe furnace. Preferably, the furnace is so charged that the proportionof lime to coke in the charge increases slowly from the furnace wallinwards to a point located at some distance beyond the tuyere mouthsafter which the lime concentration rises sharply to a maximum at thecenter of the furnace.

Variation of the lime concentration in the manner discussed effectivelyeliminates the undesired shell formation mentioned above. Additionally,it has been found that a substantially more efficient reaction isobtained. These improved results can perhaps be explained by thefollowing discussion. Three distinct regions may be noted in a shaftfurnace with tuyeres through which an oxygen-rich blast is infilled withsolid fuel and equipped.

2,880,009 Patented Mar. 31, 1959 jected as a result of the combustionand gasification of the solid fuel. These regions are (l) combustionzone in the vicinity of the tuyeres; (2) an adjacent reduction zonewhere the CO formed is reduced to CO by the carbon that has been raisedto a high temperature, and (3) an adjoining preheating zone where therising hot gases heat the descending cold solid fuel by passing incountercurrent relation thereto.

By providing the tuyeres with sight holes, the temperature of theglowing fuel surfaces in ends may be optically measured and thetemperature at the end of the reduction zone (where the temperature ofthe gas phase is taken to be equal to the temperatureof the solid fuel)may then be calculated. It has been found that when coke is gasified ina furnace of this type with a blast composed of 47%, by volume,technical oxygen (i.e. by volume of O and 10% by volume of N and 53%, byvolume, of steam, the optically measured temperature of the glowing fuelsurface in front of the burners amounts to about 1600 C., while acalculation shows that the temperature at the end of the reduction zonewill be about 875 C. At higher oxygen contents this temperaturedifference decreases.

It is, therefore, surprising to find that if the gasification iselfected using an oxygen-steam blast with a very high oxygen content,e.g. 65% to oxygen, by volume, or a blast consisting of oxygen enrichedair with at least 35% oxygen the temperature at the end of the reductionzone is considerably higher than the measured temperature of the glowingfuel surface immediately in front of the tuyeres. For example, in a testwherein the blast consisted solely of technical oxygen, the temperaturemeasured at the glowing fuel surface in front of the tuyeres amounted toabout 3400 C., while the temperature at the end of the reduction zonewas 4000 C. Accordingly, if a mixed charge of coke and lime is fed tothe furnace and a blast with a very high oxygen content is appliedthereto, a lime particle located in the immediate vicinity of thetuyeres may have a temperature of many hundreds of degrees below that ofa lime particle in the reduction zone, dependent upon the diameter ofthe furnace. This can be more clearly understood by reference to theaccompanying drawings wherein:

Figures 1 and 2 are diagrammatic views of the effect of furnace diameteron the arrangement of the combustion, reduction and preheating zones;and

Figures 3 and 4 are sectional elevations of furnaces provided with meansfor controlling the distribution of the charge according to theinvention.

Referring more particularly to Figure l, the furnace shown therein has asmall diameter, e.g., one up to 0.5 m., and the space between thetuyeres is shown to be entirely occupied by the combustion zone which isoverlain by the reduction zone. Figure 2 shows a furnace with a largerinternal diameter, e.g., one of the order of 0.5 m. to 2 m.Consequently, in this case, there is a larger distance between the endsof two opposed tuyeres and, as shown, the space between the tuyeres, incontrast to the situation shown in Figure l, is not entirely occupied bythe combustion zone. Thus, in Figure 2, oxygen supplied through thetuyeres is entirely consumed before reaching the center of the furnaceand the reduction zone extends downwards into the region between the twoopposed tuyeres.

In the situation illustrated by Figure l, substantially all descendinglime particles will first pass through the entire reduction zone, andthey are allowed sufiicient time to be heated up to a temperature highenough to react with the carbon at a similar temperature to form thedesired carbide. However, in the case shown in Figure 2, part of thelime particles, viz., the particles located over the tuyere ends, do notpass through the reduction zone where front of the tuyere thetemperature is highest. Furthermore, the stay of these particles in thecombustion zone is relatively short due to the fact that this zone is sosmall. As a result, the lime particles are not heated up to the hightemperature (e.g., 2000 to 2200" C.) needed for the carbide formation.Some carbide is formed at the surface of the lime operating troubles.fuel combustion will 7 increased.

usual gross composition of, for example, 20-30% by Weight of CaO and80-70% by weight of C (in the form of coke) the lime content may rise,slowly at first and then more rapidly, from 0 furnace wall to 85% ofhigh lime-content in the vicinity of the tuyere mouths. Additionally, nounreacted cumulate at the furnace center.

The desired increase in the lime content of the towards the center ofthe furnace may be effected in variin Figure 3 wherein 1 denotes thefurnace. The hearth of the furnace is provided with tuyeres 2 connectedto a feed pipe for the blast. The walls of the hearth are so designedthat they may be protected against unduly high temperatures by means ofcooling water.

On the top of the furnace there is mounted a hopper 3 whose contents canbe discharged into the furnace by lowering a bell closure 4. Underclosure 4 is a distributing device 5, the position of the closure withrespect to the distributing device 5 determining the place to which thecharge will be delivered. For example, with the bell in position a, thecharge will descend from the hopper along the outer edge of the bell andthe outer wall of the device 5 and will accumulate in an outer regionagainst the furnace wall. when the bell is in position b, the tween theouter edge of the bell and the curved inner wall of the distributingdevice and accumulate in the central region around the center line. Whenthe bell is put in position 0, the charge is delivered to the medialregion between the central and outer regions aforesaid. By releasingsuccessive quantities of material differing in slowly and then rapidly,from the furnace wall towards the center.

The same result may alternatively be obtained in another way, namely, bymaking use of the segregation which occurs when the charge is composedof carbon particles and lime particles of different sizes. The specificgravity of carbon in the form of coke is considerably different fromthat of lime, namely, 0.5 for coke and 1.5 for lime. Accordingly, if acoke-lime mixture, in which the lime particles are smaller than the cokeparticles, is supplied from a hopper through a centrally arrangedvertical feed pipe into a furnace with an internal diameter segregationwill be. The relationship of the diameter of the centrally arranged feedpipe and the furnace diameter also has an influence on the ultimatecoke-lime distribution in the furnace charge. For example, to obtain theouter region The effect of Composition of the blast:

35% by volume of steam 65% by volume of technical oxygen (contaminatedwith by volume of N Reaction mixture: 1 part by weight of lime and 2parts by weight of coke Amount of blast: 500 m. per hour Enteringvelocity of the blast: 80 m./sec.

Height of bed over the tuyere mouths: times larger than the cokediameter In contrast to the foregoing, the above operations wererepeated, except that the furnace was fed with a charge comprising cokehaving a particle diameter of -60 mm. and lime with a particle diameterof 10-20 mm. The resulting filling was such that the lime concentrationincreased inwardly towards the center of the furnace and a carbide witha CaC -content of by weight was continuously produced without anydifficulty.

Various modifications in the invention as described above can be madewithout in any way deviating from the scope thereof as defined in thefollowing claims wherein I claim:

1. In a process for the production of calcium carbide in a verticalshaft furnace in which a charge of lime and carbonaceous fuel is heatreacted while passing downwardly therethrough with a gas blast of highoxygen con tent introduced into the lower part of said furnace throughtuyeres so as to gasify said fuel and provide the temperature and energynecessary for carbide formation, the improvement which comprisesmaintaining, in a zone immediately above said tuyeres, a distribution oflime in said charge which gradually and continuously increases from aminimum concentration of lime adjacent the furnace wall to a maximumconcentration of lime in the region of the axial line of said furnace byaxially feeding a charge of intermixed lime and carbonaceous fuelparticles into said furnace wherein the average maximum dimension ofsaid lime particles is less than onehalf the size of said fuel particleswhereby disposition of a shell formation of lime on the furnace walladjacent said tuyeres is substantially avoided. I 2. The improvedprocess of claim bonaceous fuel is coke.

3. The improved process of claim 1 wherein the concentration of limegradually increases from substantially zero concentration at the sidesof the furnace to about by weight at the center.

4. The improved process of claim 1 wherein the concentration of limeincreases slowly from the sides of the furnace for a distance and thenincreases rapidly to about 85% concentration at the center.

5. The improved process of claim 1 where the oxygen content of saidblast is from 65 to by volume by using oxygen-steam blast.

6. The improved process of claim 1 wherein the oxygen content of saidblast is at least 35% by using as blast oxygen-enriched air.

1 wherein said car- Belgium Feb. 15, 1954 Canada Aor. 13. 1954

1. IN A PROCESS FOR THE PRODUCTION OF CALCIUM CARBIDE IN A VERTICALSHAFT FURNACE IN WHICH A CHARGE OF LIME AND CARBONACEOUS FUEL IS HEATREACTED WHILE PASSING DOWN WARDLY THERETHROUGH WITH A GAS BLAST OF HIGHOXYGEN CONTENT INTRODUCED INTO THE LOWER PART OF SAID FURNACE THROUGHTUYERES SO AS TO GASIFY SAID FUEL AND PROVIDE THE TEMPERATURE AND ENERGYNECESSARY FOR CARBIDE FORMATION, THE IMPROVEMENT WHICH COMPRISESMAINTAINING, IN A ZONE IMMEDIATELY ABOVE SAID TUYERES, A DISTRIBUTION OFLIME IN SAID CHARGE WHICH GRADUALLY AND CONTINUOUSLY INCREASES FROM AMINIMUM CONCENTRATION OF LIME ADJACENT THE FURNACE WALL TO A AXIAL LINEOF SAID FURNACE BY AXIALLY IN THE REGION OF THE AXIAL LINE OF SAIDFURNACE BY AXIALLY FEEDING A CHARGE OF INTERMIXED LIME AND CARBONACEOUSFUEL PARTICLES INTO SAID FURNACE WHEREIN THE AVERAGE MAXIMUM DIMENSIONOF SAID LIME PARTICLES IS LESS THAN ONEHALF THE SIZE OF SAID FUELPARTICLES WHEREBY DISPOSITION OF A SHELL FORMATION OF LIME ON THEFURNACE WALL ADJACENT SAID TUYERES IS SUBSTANTIALLY AVOIDED.